Method and Device for variable motion and applications using Interchangeable Heads

ABSTRACT

A machine for automating manual labor has a motor portion, transmission portion, and a head portion which may all be interchanged with alternates for different applications. The machine is driven by an electric motor that can perform different motions and actions, one at a time or simultaneously, depending on the transmission and head portions. Two such motions are rotary and linear reciprocating motion. Applications include cleaning surfaces, cleaning vessels, mixer, blender, chopper, slicer, shredder, vibrator, massager, semi and fully automatic milk cream maker.

This is a continuation-in-part of U.S. application Ser. No. 11/824,331, filed Jul. 2, 2007.

FIELD of the INVENTION

This invention is in the field of tools and household appliances.

BACKGROUND OF THE INVENTION

There is a lack in the known art of a compact hand-held device that can both rotate, and provide linear reciprocating motion; generally either one or the other type of motion is possible when using a single tool.

For example U.S. Pat. No. 5,450,646 to McHugh provides an electrically rotating brush. However this apparatus enables only rotation movement of the brush attachment.

On the other hand reciprocating tools such as sanders are known, which provide only linear reciprocating motion. The invention comes to remedy the fact that only one or the other motion is delivered from a given tool.

SUMMARY OF THE INVENTION

It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and, together with the description, serve to explain the principles and operations of the invention but the not to limit the invention to these descriptions only.

The object of the present invention is to overcome the shortcoming of prior art cleaning devices by allowing for both rotational and linear reciprocal motions from the same motor. These various motions are of use for rubbing, polishing, sanding, and brushing operations.

The device comprises two or three sections. In those embodiments utilizing three sections these are a motor section, a transmission section, and a head section. These sections are modular and easily replaceable, allowing fast and simple switching of head, transmission, or motor depending on the necessary task (i.e. either for rotary motion or linear reciprocating motion).

The head may comprise various materials like “Scotch”™ or others abrasive materials, polishing materials, cutting elements such as disks or blades, and the like.

The device can be operated without electric power in the manner of a simple cleaning brush or may be operated using the electric motor with either battery or external power supply. The apparatus can be used to scrape whitewash or paint signs from pavements, walls or other home utensils.

Another application of the present invention relates to the preparation of whipped milk. The present known method of producing milk foam is based on the heating of the milk and producing bubbles by using hot steam—this process is controlled manually and the quality of the milk foam is very much affected by the proficiency of the user. This process requires a specific combination of adequate heating process and specialized usage of the steam.

The inventive process uses an embodiment of the device for production of high quality consistent milk foam with a manual or automated procedure.

An additional application of the present invention is for kitchen use (as a mixer, blender, chopper, and other food processor roles). The interchangeable head equipped with a rotary blade or with a rotary disk for instance allows slicing, shredding, or chopping/mixing.

A further application could be a vibrator/massager that is based on a reciprocating and rotating movement.

A key element of the invention is that it allows for changing the motion of the machine by exchanging the head portion. Possible motions include circular motion, eccentric motion, linear reciprocating motion, and combinations of these.

In a semi-automatic milk-foaming embodiment, one uses a whipping head attached to the motor and a linear movement combined with rotational motion is obtained. At one stage in the process the milk is heated, which is accomplished externally from the machine of this invention.

In an automatic milk-foaming embodiment, a free standing machine with a program and microprocessor is used along with a heating element and temperature sensors in addition to the basic machine of this invention. This embodiment produces the end product by whipping, heating, and subsequent further whipping of the milk according to a predetermined series of actions controlled by the microcontroller.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain by way of example only, the principles of the invention:

FIG. 1 shows cleaning apparatus with the main portion and a replaceable cleaning head in accordance with one the preferred embodiments.

FIG. 2 shows the main portion of the apparatus together with the transmission means.

FIGS. 3 a and 3 b show respectively the main portion with mounted thereon cleaning head in its forward most and rearmost position.

FIG. 4 shows exploded view of the cleaning apparatus with the main portion and rotary replaceable cleaning head in accordance with the second embodiment.

FIG. 5 shows the cleaning apparatus equipped with the rotary cleaning head.

FIGS. 6,7 show respectively an enlarged view in cross-section of a portion of the apparatus shown in FIG. 5.

FIG. 8 shows an enlarged view of the two-way threaded screw.

FIG. 9 shows an application as a vibrator.

FIG. 10 shows an application as a hand held semi-automatic whipped milk maker.

FIG. 11 depict an application as a sander.

FIG. 12 show an application for a rotary tool.

FIGS. 13 a, 14 b, 14 c, 14 d, 14 e, 14 f show different applications using the main portion with the set of interchangeable heads, one at a time.

FIGS. 13 c,d,e,f show an embodiment of this invention where the oscillation motion is caused by a two-way threaded screw and the rotating movement is achieved by a screw connection to the motor shaft.

LEGEND FOR FIGURES

-   1 a main portion -   2 an interchangeable head -   3 a housing -   4 a motor -   5 an on/off knob -   6′ electrical cord -   6 appropriate plug -   7 transmission means -   8 motor's shaft -   9 screw -   9′ screw -   10 spiral -   11 reciprocating (oscillating) shaft -   12 a sleeve portion -   13 pin -   16 spring -   17 forward most portion -   18 rough pad -   19 forward cylindrical portion -   20 ball bearing -   21 ball bearing -   22 rear-most portion -   23 disposable cleaning roughened attachments -   24 an internal driven cup -   25 interchangeable head for rotation -   26 a torque transmission pin -   27 a plane for transmitting torque -   28 disk -   30 a left and right screw -   32 a leaf or rider -   34 cylindrical transmission -   35 length of protrusion -   36 housing of embodiments -   37 a rotating head -   38 oscillating head -   39 the end of the working rotating shaft -   40 the end of working reciprocating shaft -   41 rotating shaft -   42 working reciprocating shaft -   43 oscillating and rotating head -   50 massage device -   51 switch -   52 center -   53 motor massage -   54 double screw massage -   55 applicator -   60 handle -   61 protecting disk -   62 section -   63 whipping shaft -   64 plate with many holes -   65 container

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As will be appreciated the present invention is capable of other and different embodiments than those discussed above and described in more detail below, and its several details are capable of modifications in various aspects, all without departing from the spirit of the invention. Accordingly, the drawings and description of the embodiments set forth below are to be regarded as illustrative in nature and not restrictive.

FIG. 1 shows a cleaning apparatus suitable for example, for cleaning a baking pan. The apparatus according to the first embodiment of the invention includes a main portion 1 and an interchangeable head 2 with a reciprocating (oscillating) shaft 12 seen in FIG. 3. Main portion 1 consists of a housing 3 and a motor 4 seen in FIG. 2 mounted therein.

The motor residing in housing 3 is operated from an internal source or an external one. An on/off knob 5 is supplied for controlling electrical power to the motor 4 seen in FIG. 2.

FIG. 2 shows the motor and transmission parts. For convenience cordless rechargeable battery could be used and in this case the apparatus could be equipped with appropriate plug 6 or it can be provided with an electrical cord 6′ connected to a wall mounted unit. The removable transmission means 7 is connected to motor's shaft 8 via screws 9 and 9′. The removable transmission means 7 is removed when an interchangeable head (for example from FIG. 13) is attached to the main portion 1. Rotational motion of the shaft effected by the motor is transferred to spiral surface 10 of the transmission. The spiral surface 10 cooperates with pin 15 seen in FIG. 3 of the reciprocating sliding shaft 12 of the head and causes a reciprocating (oscillating) motion thereof.

The transmission portion 7 may consist of a cam as seen in FIGS. 1,2. This cam may in fact be adapted to impart a linear reciprocating motion of arbitrary time dependence to said head portion; since the linear position of the head portion depends on the rotational position of the cam, the height profile of the cam will determine the time dependence of the linear position of the head portion. Thus unusual and arbitrary time dependences may be obtained, for example extreme accelerations, minimized jerk, and the like.

FIGS. 3 a and 3 b show the main portion 1 with the interchangeable head 2 with oscillating shaft 12 connected for lateral insertion and retention.

FIG. 3 a shows the position of the shaft 12 as it is pushed to its extremity in a forward direction the pin 15 being pushed by the spiral transmission 7 as the transmission 7 turns. In this position the spring 16 is compressed.

FIG. 3 b shows the position of the shaft 12 is in its extreme back position as the spiral transmission 7 continues to turn and the pin 15 is no longer pushed by the transmission 7. The spring 16 is free to expand and push the pin 15 and shaft 12 to a rear most position. As the transmission 7 continues to turn, the above movement is repeated many times a minute thereby imparting a reciprocating motion to shaft 12 and all that is attached thereto.

Interchangeable head 2 includes in its forward part a sleeve portion 13 seen in FIG. 1 in which sliding shaft 12 reciprocates. The forward end of the reciprocating shaft 12 seen in FIG. 3 carries the forward most portion 17 comprising a rough pad 18 as seen in FIG. 1.

A sliding shaft is provided with adjusting means 14 as seen in FIG. 1 having a pin 15 as seen in FIG. 1 at its rear end. The shaft slides within the head 2.

The reciprocating motion thereof can be adjusted via pin 15.

Transmission 7 could be made of hardened steel and is used for coupling motor's shaft to both interchangeable heads and for submitting to them either the reciprocating linear motion or rotating motion.

The transmission 7 can push the sliding shaft 12 forward and backward within the sleeve against a retaining spring 16 bearing against a stop in head's housing.

The forward most portion 17 as seen in FIG. 1 of cleaning head 2 is coated partially with rough pad 18 which cleans a desired surface.

The connection of the main portion 1 with interchangeable head 2 causes the pin 15 to touch coupling's spiral surface 10, so producing linear oscillation at the head from rotary movement of the motor. The forward linear displacement is reversed on the down stroke due to retaining spring 16 which forces sliding shaft 12 back.

FIG. 3 a shows the sliding shaft at its forward position and FIG. 3 b at its backward position according to previous description.

The given description leads to the understanding that adjusting means 14 seen in FIG. 1 attached to the sliding shaft 12 (FIG. 3) can be adjusted via a screw in order to establish the sliding amplitude of the forward part of sliding shaft equipped with rough pad 18.

FIGS. 4-6 show the cleaning apparatus according to a second embodiment implementing rotary movement of the interchangeable head.

FIG. 4 shows interchangeable head 25 with rotary shaft 11 seen in FIG. 5 mounted within the head. Disk 28 is mounted on the forward cylindrical portion 19 of the head, which can rotate together with the rotary shaft 11 seen in FIG. 5. The shaft is mounted by virtue of two ball bearings 20 and 21 seen in FIG. 5 within the head and it goes there through from the rear-most portion 22 seen in FIG. 4 of the cleaning head to the forward most portion thereof.

In some embodiments a disposable cleaning attachment 23 may be attached to the disk for instance by use of adherent material, the cleaning attachment in some embodiments comprising abrasive elements such as sandpaper.

FIG. 5 shows the main portion 1 with interchangeable head 25 for rotation carrying rotating shaft 11.

The rotating shaft 11 is centrally mounted with respect to the longitudinal axis of the head 25 by virtue of an internal driven cup 24 seen in FIG. 6 and bearings 20 and 21. When coupled to the main portion the cup is rotated by the transmission 7, it in turn rotates the rotating shaft 11. Given that the rear-most portion of the shaft 11 is provided with a thread, the cup 24 can be fixed thereon and thus rotation can be transferred from the cup 24 to the shaft 11. The inwardly facing cylindrical surface of the cup 24 is provided with a torque transmission pin 26 seen in FIG. 6, directed radially respect thereto. The transmission 26 is provided with a plane 27 seen in FIG. 6 a for transmitting torque. By virtue of interaction between the pin 26 and plane 27 seen in FIG. 7, rotation is transmitted from the transmission means to the shaft.

FIGS. 6 and 7 show sectional views of the transmission 7 cooperating with a plane 27 for transmitting torque via pin 26 to the driven cup 24 which in turn transmits torque to rotary shaft 11 seen in FIG. 5. The shaft may include a variety of tools attached to the end, such as a holding plate 23 that holds a sanding disk 28.

Motor portion 1 can be mated with various working heads either for linear or rotary motion, or combinations, allowing significant improvement to for example cleaning work. By virtue of the above design the apparatus is efficient, compact, easy in use and cheap. Disposable working attachment pads can be attached e.g. via glued paper on one surface thereof, Velcro fitted both to working heads and cleaning device, or the like. This arrangement allows fast and easy replacement of worn working pads for effective cleaning work.

FIG. 13 shows embodiments for reciprocating movement while rotating also within provision of the invention. Such embodiments can be built for example as follows. Attaching simultaneously two shafts, one to the screw 30 the rotating shaft 41 and the second to the cylindrical transmission the working reciprocating shaft 42 causes simultaneously rotating and oscillating movements of the shafts. The electrical cord 6 could be attached to a battery source or to an isolated transformer connected to line voltage.

The transmission means in certain embodiments are based on a unique doubly threaded screw component 30 seen in FIG. 8. This is a threaded rod or cylinder having two threads along its length, one of right handed helicity and the other left handed. A leaf or rider 32 is located on the screw 30 (that is fastened to the housing 3 (FIG. 13 c) that includes motor 4 (seen in FIG. 1) between the screw 30 and the cylindrical transmission 34.

This unique screw allows direct transfer of rotational motion from motor to head in one mode, transformation of rotary motion of the motor shaft to linear reciprocating motion of the cylindrical transmission in another mode, and both linear and rotational motion in a third mode. Eccentric motion is provided in a fourth mode, and combinations of the above motions are further possible simply by allowing or preventing certain degrees of freedom between rider and head portions of the device, and depending on where the head portion attaches to the rider.

Circular motion is obtained when a leaf or rider 32 (FIG. 8) serving as coupling between the doubly-threaded screw and the head section is clamped to the screw (allowing no relative motion between rider and screw) such that it rotates therewith. Eccentric motion of the head is obtained using the same clamped screw if the head section is attached to the rider not at the center of rotation of the screw but at some nonzero radius away from the center of rotation.

This unique screw allows transformation of rotary motion of the motor's shaft to linear reciprocating motion of the cylindrical transmission in certain modes, and both linear and rotational motion in other modes. Reciprocating motion is obtained when the cylindrical transmission 34 is prevented from rotating while being allowed to move along a predetermined path inside the housing 36 by means of limiting its degrees of freedom as is known in the art (see FIGS. 13 d,e,f).

Reciprocating motion is obtained when the cylindrical transmission 34 is prevented from rotating while being allowed to move along a predetermined path inside the housing 36 by means of limiting its degrees of freedom as is known in the art.

Alternatively in order to achieve reciprocating motion the cylindrical transmission 34 is moved by a length of protrusion 35 that reciprocates within the inner part of the housing 36 while preventing the rotary motion of the cylindrical transmission 34. The protrusion 35 sits in a matching groove on the inside of housing 36.

The leaf or rider 32 may move from one end (start point) of the screw 30 to the opposite end (end point). The leaf or rider's 32 change of direction happens upon reaching the end of its travel along one helix of the double screw 30; it begins travel in the opposite direction along the second oppositely-handed helix (from left handed to right handed screw or vice versa) since the ends of the screw thread grooves are coupled at each end, thus allowing an oscillating motion of the cylinder transmission 34 moving inside the housing 36.

FIG. 8 shows an enlarged view of the two way screw 30. The leaf or rider 32 rides on one side of the double threaded screw. The motor turns the shaft and the shaft turns the screw 30. When the leaf or rider 32 reaches the end of the thread of screw 30, the leaf or rider 32 automatically is guided to the other thread side, since the thread groove is so cut to connect the right-hand thread to the left-hand thread at both ends of the screw. Thus as the motor turns the shaft, the leaf or rider 32 reciprocates, changing direction each time the leaf or rider 32 reaches the end of the thread of screw 30. The leaf or rider 32 is attached to the cylindrical transmission FIG. 13 c and thereby the reciprocating motion is transferred to the head that is desired to reciprocate.

As will be appreciated by one skilled in the art the rider may also be in direct mechanical communication with the head portion thereby providing both rotational and linear reciprocating motions to the head.

As will further be appreciated by one skilled in the art the rider may also be put in solely linear mechanical communication with the head portion, thereby imparting linear reciprocating motion only. This may be done by utilizing a coupling between the rider and head portion that allows rotational slippage but not translational slippage, for example by means of a slip ring.

As will be still further appreciated by one skilled in the art, the rider may also be put in rotational mechanical communication with the head portion thereby imparting rotational motion to the head portion. This may be accomplished by using a coupling between rider and head portion that allows translational slippage but not rotational slippage, for example by means of a grooved shaft in which the rider travels.

It will be still further appreciated by one skilled in the art that the rider may be put in eccentric rotational mechanical communication with the head portion thereby providing eccentric rotational motion to the head portion, by means of a suitable coupling between rider and head portion.

FIG. 9 shows a side view of an embodiment of this invention as a massage device 50 or vibrator where the user could choose to utilize rotational motion, linear oscillating motion, or both motions at the same time. These different effects could be operated using the switch 51. The rotation motion could be turned into a vibration by the connection between the motor shaft and the applicator 55 to be off center 52 in the applicator. The motor 53 provides the rotational force.

The housing of the motor 53 would also act as the handle for the device. The double screw 54 would turn the rotational force of the motor 53 into a linear back and forth reciprocating motion as described in relation to the embodiments in FIG. 13. The applicator 55 could be made for example, hard and smooth or somewhat flexible material as is necessary to provide the desired effect for the user.

FIG. 10 shows the application of this invention as a semi-automatic hand-held milk whipping machine. The mechanical operation of this embodiment is as described in FIG. 13 where the device produces a reciprocating motion. The motor is housed in the handle 60. A splash protecting disc 61 prevents milk splashing onto the handle 60 or outside container 65. The double threaded screw could be housed in section 62. At the distal end of the shaft 63 is at least one plate 64 with many holes therein. The sectional shape of container 65 would preferably be like the shape of the holed plate 64 and a little larger in size to facilitate the plate 64 moving up and down in the container 65.

When the motor is switched on the holed plate 64 would move up and down in pre-heated milk and that motion would create whipped milk. As mentioned there is also provision for rotational motion in addition to linear reciprocating motion, simultaneously.

The milk could be heated again to produce a higher quality milk foam product.

FIG. 11 and FIG. 1 depict an application as a sander. FIG. 1 shows transmission mechanism 7 attached to the motor, while FIG. 11 shows it removed, allowing a different transmission mechanism (for example rotary vs. linear) to be substituted.

FIG. 12 and FIG. 4 show an application for a rotary tool. FIG. 4 shows transmission mechanism 7 attached to the motor, while FIG. 12 shows it removed, allowing a different transmission mechanism (for example linear vs. rotary) to be substituted.

FIGS. 13 a,b,c,d,e,f show various applications using the main portion with a set of interchangeable heads for rotary or linear or both linear and rotational motion in a third mode, one interchangeable head at a time.

Examples of rotating and reciprocating heads are seen in FIGS. 13 d and 13 e respectively.

In FIG. 13 d, a rotating head 37 contains the rotating shaft that is connected to the screw 30 that causes rotary motion of the shaft. Velcro material could cover the end 39 of the working rotating shaft.

In FIG. 13 e, the oscillating head 38 contains the oscillating shaft. Velcro material could cover the end 40 of the working reciprocating shaft.

The reciprocating shaft 42 seen in FIG. 13 e is attached to the cylinder transmission that causes the reciprocating movement of that shaft. Hence the amplitude of the reciprocating shaft depends on the screw's 30 length.

FIG. 13 f shows the oscillating and rotating head 43. Attaching simultaneously two shafts, one to the screw 30 the rotating shaft 41 and the second to the cylindrical transmission the working reciprocating shaft 42 causes simultaneously rotating and oscillating movements of the shafts. The electrical cord 6 could be attached to a battery source or to an isolated transformer connected to line. 

What is claimed:
 1. An apparatus for achieving a variety of rotary motion, linear motion and simultaneously rotary and linear motions via two axes used for cleaning dirty, singed and oily surfaces of kitchen utensils and for preparing whipped milk, said apparatus comprising, a. a motor portion operatively producing a rotational force; b. a transmission mechanism configured to convert said of rotational force of said motor into a preconfigured operational motion c. an interchangeable head-piece having a housing, a distal end and a proximal end d. wherein said preconfigured operational motion is selected for the group consisting of linear motion, rotary motion and a combination of linear and rotary motions; e. wherein said head-piece, coupled with a said respective transmission mechanism, is adopted to receive either a linear motion, or a rotary motion, or a combination of linear and rotary motions; f. wherein said proximal end of said head-piece is securely attached to the housing of said motor; g. wherein said distal end of said head-piece is a functionary portion; and wherein h. the said preconfigured operational motion activates said functionary portion i. head section, said modified motion being selected from the group consisting of: rotational motion; eccentric rotation; linear reciprocating motion; and combinations thereof; j. wherein said motor, head, and transmission portions are replaceable allowing for a variety of tools and motions to be implemented.
 2. The device of claim 1 wherein one of said transmission portions comprises a double-threaded screw whose threads have opposite helicity and are joined at each end, and a rider adapted to travel upon a first thread of said screw in a first direction until reaching a first joint between said two threads, whereupon said rider travels along the second thread of said screw in the opposite direction from said first direction until reaching a second joint between said threads, whereupon said rider will travel upon the first thread of said screw in said first direction again.
 3. The device of claim 2 wherein said rider is in direct mechanical communication with said head portion thereby providing both rotational and linear reciprocating motion.
 4. The device of claim 2 wherein said rider is in linear mechanical communication said head portion thereby imparting linear reciprocating motion to said head portion.
 5. The device of claim 2 wherein said rider is in rotational mechanical communication with said head portion thereby imparting rotational motion to said head portion.
 6. The device of claim 2 wherein said rider is in eccentric rotational mechanical communication with said head portion thereby providing eccentric rotational motion to said head portion.
 7. The device of claim 1 wherein said head portion and transmission portion are adapted to perform functions selected from the group consisting of: sanding; buffing; polishing; scraping; foaming; vibrating; sanding; driving screws; ratcheting; sawing; cleaning vessels, cleaning surfaces, chopping objects, slicing objects, mixing objects, massaging, vibrating, whipping milk, whipping other liquids.
 8. An apparatus for achieving rotary and linear motion as claimed in claim 1, wherein said transmission mechanism comprises a partially complete spiral cam, concentric with the drive axle of said motor.
 9. An apparatus for achieving rotary and linear motion as claimed in claim 1, and wherein said head-piece comprises: a. an axle positioned longitudinally in said head-piece, having an end riding on said spiral and at the distal end of said axle is securely attached to said functionary portion; and b. a biasing element for operatively pushing said axle back towards said motor, when said spiral turns passes the extreme forward position of said spiral, creating linear operational motion of said axle and said head-piece.
 10. An apparatus for achieving rotary and linear motion as claimed in claim 1, wherein the said head piece is operatively attached to comprise a bar across its diameter at the end closest to the drive axle of said motor whereby the said spiral catches on the said bar and causes the said head-piece to rotate as the said spiral rotates.
 11. An apparatus for making whipped liquid comprising: a. a motor portion; b. transmission means; c. a head-piece comprising attachment means allowing said head piece to attach to said motor portion and engage said transmission means, further comprising at least one disc of a predetermined thickness perforated with holes having a predetermined density and diameter; d. an axle positioned longitudinally in said head-piece adapted to transfer linear motion from said transmission means to said disc; e. a spring to push said axle and head-piece back towards said motor after said spiral has pushed said axle away from said motor; whereby rotational motion of said motor is transformed to reciprocating linear motion, thereby forcing said perforated disc back and forth thereby whipping said liquid.
 12. The device of claim 10 wherein said transmission means selected from the group consisting of a spiral cam.
 13. A method of obtaining a variety of motions comprising steps of: a. providing a motor portion comprising a motor; b. providing a head portion; c. providing a transmission portion adapted to transfer rotational motion of said motor to a modified motion of said head section, said modified motion being selected from the group consisting of: rotational motion; eccentric rotation; linear reciprocating motion; and combinations thereof; d. causing said motor portion to rotate thereby imparting a modified motion to said head section; wherein multiple possible motions of said head portion are obtained, and wherein said motor, head, and transmission portions are replaceable allowing for a variety of tools and motions to be implemented.
 14. The method of claim 12 wherein said transmission portion comprises a double-threaded screw whose threads have opposite helicity and are joined at each end, and a rider adapted to travel upon a first thread of said screw in a first direction until reaching a first joint between said two threads, whereupon said rider travels along the second thread of said screw in the opposite direction from said first direction until reaching a second joint between said threads, whereupon said rider will travel upon the first thread of said screw in said first direction again. 